Such systems have a freeze-up problem when the aircraft flies at high altitudes or when the aircraft is parked outside at freezing temperatures, unless the water supply system has been drained. Heretofore, it has been customary to electrically heat at least those portions of the supply system which may become exposed to freezing temperatures. The supply of electrical energy to a parked aircraft may cause problems on the one hand. On the other hand, it may not be desirable to drain the water system, especially if the aircraft is parked only temporarily.
Further, the heating systems for these water pipes required a substantial expense for temperature sensors and controlled heating elements arranged along those portions of the supply pipe system which are most likely exposed to freezing temperatures.
Further, prolonged parking of an aircraft requiring drainage of the system is normally performed under the influence of gravity which means that all the supply pipes must be installed with a slant downwardly toward a drainage port. Such installation requirement for the supply pipes is undesirable, because it interferes with the installation of the same water supply system in aircraft model variations having different body lengths. In such case it is necessary to redesign the pipe system for each aircraft model separately in order to assure the required slant toward a drainage port. Both, the high energy consumption for heating the supply pipes and the installation requirements for gravity drainage are undesirable.